Loudspeakers (also denoted as “Audio Speakers” or simply “Speakers” for brevity) for converting electrical signals into sound are very well known in the art. Speakers may generate an electromagnetic signature that, in some applications, interferes with the intended function of various devices and sensors that sense electromagnetic fields. For example, in devices for detecting and measuring magnetic field signals (e.g., utility locator devices, electromagnetic frequency meters, devices with magnetometers or other magnetic sensors, and the like) the frequency range of the electromagnetic signature emitted by audio speakers may coincide or overlap with the frequency range of electromagnetic energy being detected and measured by such devices. Consequently, the electromagnetic signature of the speakers may interfere with measurements made by these devices, resulting in distorted or otherwise inaccurate measurements.
Speakers with magnetic field cancellation have been known in the art. For example, in many audio speakers, the magnetic field emitted by permanent magnets in the speaker driver (e.g., in a speaker with a convention magnet and coil construction) is canceled by shielding. However, existing speakers typically do nothing to cancel magnetic fields from the driver's voice coil caused by current flows therein. As a result, conventional speakers, even with shielding, can generate electromagnetic signatures that interfere with sensitive magnetic field detection devices such as utility locators.
Piezoelectric speakers can produce smaller electromagnetic signatures at the driver, but are typically driven at voltages that cause an interfering electromagnetic signature at the power supply. Further, many piezoelectric speakers fail to produce the quality of dynamic sound across the full range of frequencies heard by humans.
As such, magnetically canceling audio speakers known in the art fail in magnetic field sensing applications by generating an interfering electromagnetic signature, failing to provide quality dynamic sound, or both. Accordingly, there is a need in the art to address the above-described as well as other problems related to producing quality dynamic sound while having a small electromagnetic signature.